1. Field of the Invention
This application relates to an improvement in apparatus for mixing the ingredients of two component magnetic developer material used within the dry developing apparatus of a typical office copying machine. Mixing devices in various auger form are used for combining dry marking and ferromagnetic carrier constituents. Both developer components are mixed to form a specific dry developer formula composed of a predetermined ratio of marking to iron carrier constituents. The desired developer composition is best accomplished by mixing auger members arranged within the lowermost, sump portion of the dry developing apparatus. During the course of mixing, the auger mixer arrangement also contributes to providing the so-called triboelectric charging effect to the marker-carrier constituent, which enables image development.
There are provided in the dry developing apparatus two separate subsystems that provide major functions required in the operation of the developing unit. The primary portion of the developing system is comprised of various mechanical apparatus which is suspended within the pan-shaped enclosure comprising the basic developing unit framework. The pan is designed to minimize spillage of dry particulate material due to mixing, circulation and general operation. The developing unit pan also has appropriate journals located in the end frames intended to suspend various rotatably driven mixing, distribution, circulation, and developer application members.
The mixing auger members are located in the developing unit pan, usually in the sump portion, and are intended to circulate and distribute the carrier while also intermixing dry marker constituent into the carrier constituent. The marker or, as otherwise known in the xerographic art, toner, is regularly dumped into the vicinity where the mixing auger members revolve, by a toner dispensing system. The dispensing system comprises the second functional developing unit subsystem and has rotating apparatus included to dump the marker in a regular, evenly distributed amount while the copier machine is in operation.
During continuous cycles of operation of the copier machine, images are endlessly developed according to operator demand. The actual physical image development occurs continuously according to demand at the process station development zone. The developing apparatus, and more specifically, the magnetic applicator roller within the apparatus, continuously applies a predetermined amount of developer to the oncoming images, which are previously exposed upon a photoconductor member, by operating means associated with illumination and image translation arranged for the purposes of projecting the original document image.
The marker is carried to the development zone by the ferromagnetic carrier constituent, the virtues of which are well known in the xerographic art. Within the applicator roller, one of numerous magnets cause the ferromagnetic carrier particles to bristle radially outward from the applicator roller surface. In so doing, the bristle, or brush, engages the photoconductor image carrier surface and the electric differential in charge potential between exposed latent image and charged marker particle constituent renders a physical marker transfer and attachment to the exposed latent photoconductor image, thereby causing the visual image development on the photoconductor. In this manner and from this position, the visual marked image is carried on the photoconductor to a transfer station, also part of the overall copier process, where the image is then caused under influence of electrical potential to physically migrate to a piece of copy paper. The resulting transposed image copy is then directed through a fusing station which permanently fixes the image to the copy sheet.
The developing process continues upon repeated cyclic operation of the copier machine, as required by the machine operator. Due to repeated endless operation, there is, however, a concern regarding abrasive wear of the ferromagnetic marker-carrier constituent. The carrier constituent is endlessly recycled within the developing apparatus in order to reaccumulate a fresh supply of marker after deposition at the development zone in the course of image development. Recycling the carrier constituent is provided through developing unit apparatus which rotatively mixes, circulates, and causes a general stream-like flow of carrier with attached marker to the development zone. In one portion of the cycle, the carrier constituent is empty, or relieved of marker, and is caused to slide down an inclined ramp to the mixing zone admidst revolving augers.
During the course of the endless cyclic motion that the carrier is subjected to, there is of course a great deal of abrasive rubbing of carrier particles on the developing unit pan and against revolving elements which impart the flow of developer. This rubbing and abrasive action eventually wears the fiber-like carrier particles until they become smaller in size, having been worn down in effect to a rounded shape. The abrasion, reduced size, and rounded shape all combine to reduce the effectiveness of the carrier.
The initial stages of developer preparation begins at the mixing auger station in the developing unit sump where the two separate developer constituents are mixed together by a combined radial and axial tumbling action. From this point, and in pursuit of gathering a constant flow of mixed developer, a rotating magnetic applicator roller attracts developer from the nearest revolving mixing auger. The developer is pulled across the sump pan floor by the magnetic applicator roller and attaches to the roller's outer cylindrical surface in a bristle-like form.
While remaining attached to the rotating applicator roller, the developer is then pushed against a narrow aperture arranged to engage the bristled developer. The aperture acts as a doctoring device and restricts or limits to a desired amount the developer to be applied at the development zone. During further rotation of the applicator roller, the developer in bristle form stands radially outward from the roller and engages the photoconductor member, usually arranged to move in an opposing relative direction with respect to the applicator roller.
Of course, the carrier constituent is relieved of marker at the development zone due to the marker development transfer process, but carrier remains attached to the magnetic applicator roller until it rotatably travels attached to the magnetic roller to the developing apparatus carrier stripper bar. At the carrier stripper bar, which is a fixed, non-moving blade-like member, arranged in close proximity to the applicator roller, the carrier is physically sheared off the roller. Finally, the detached carrier then slides down an inclined ramp under the influence of gravity to the point of origination admidst the rotating mixing auger members.
Within the developing apparatus mixing auger station, a fresh supply of marker is re-accumulated by the iron carrier constituent in order to provide the development system with an endless flow of developer at the development zone. The marker is also supplied endlessly in separate predetermined amounts by the toner dispensing apparatus. This marker dispensing apparatus is intentionally arranged within the developing apparatus so that it dumps marker directly between the revolving mixing auger members arranged beneath the dispenser apparatus.
2. Prior Art
U.S. Pat. No. 4,146,323 discloses the use of augering means within a developing apparatus to facilitate active crossmixing of the developer material. In particular, this patent discusses the need for active crossmixing of developer material, while the patent also provides a means of exemplifying the developer mixing process through the use of twisted, elongated auger blades having spaced slots along the helical edges of the auger blades.
U.S. Pat. No. 3,333,566 also describes an auger mixing means for a developing unit. Therein, the Inventor describes the use of simple strips of metal, twisted into auger shape and driven by meshing gears.
Accordingly, this present invention is aimed at a further improvement in the use of auger blade mixing devices for developing apparatus systems used within office copiers, the improvement being aimed at the extension of useful ferromagnetic carrier life through specific improvements in auger blade geometry.